Different kinds of extruded composites containing wood fibre and polymers are known. These composites can be used especially as constructing materials. CN 101077916 A describes one such material. It consists of 29-70 w-% of plastic, 28-69 w-% of wood fibre, 1-2 w-% of cross-linking agent, and 1-2 w-% of coupling agent. The plastic may be polyethylene, non-toxic polyvinyl chloride, or polypropylene. The wood fibre may be plant root, branch, leaf, bark, peanut shell, wheat straw, or sawdust.